ltk/org.eclipse.statet.ltk.ui/src/org/eclipse/statet/ltk/ui/sourceediting/SourceEditorViewer.java - statet/org.eclipse.statet-ltk - Git at Google

 /*=============================================================================#
  # Copyright (c) 2013, 2020 Stephan Wahlbrink and others.
  #
  # This program and the accompanying materials are made available under the
  # terms of the Eclipse Public License 2.0 which is available at
  # https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
  # which is available at https://www.apache.org/licenses/LICENSE-2.0.
  #
  # SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
  #
  # Contributors:
  #     Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
  #=============================================================================*/

 package org.eclipse.statet.ltk.ui.sourceediting;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.BadPositionCategoryException;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IPositionUpdater;
 import org.eclipse.jface.text.IRegion;
 import org.eclipse.jface.text.ITextSelection;
 import org.eclipse.jface.text.JFaceTextUtil;
 import org.eclipse.jface.text.Position;
 import org.eclipse.jface.text.information.IInformationPresenter;
 import org.eclipse.jface.text.source.IOverviewRuler;
 import org.eclipse.jface.text.source.IVerticalRuler;
 import org.eclipse.jface.text.source.SourceViewerConfiguration;
 import org.eclipse.jface.text.source.projection.ProjectionViewer;
 import org.eclipse.jface.viewers.ISelectionChangedListener;
 import org.eclipse.jface.viewers.SelectionChangedEvent;
 import org.eclipse.swt.custom.StyledText;
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.widgets.Composite;

 import org.eclipse.statet.ecommons.text.core.util.NonDeletingPositionUpdater;


 public class SourceEditorViewer extends ProjectionViewer {


 	/**
 	 * Text operation code for requesting the outline for the current input.
 	 */
 	public static final int SHOW_SOURCE_OUTLINE=            51;

 	/**
 	 * Text operation code for requesting the outline for the element at the current position.
 	 */
 	public static final int SHOW_ELEMENT_OUTLINE=           52;

 	/**
 	 * Text operation code for requesting the hierarchy for the current input.
 	 */
 	public static final int SHOW_ELEMENT_HIERARCHY=         53;


 	public static final int VARIABLE_LINE_HEIGHT= 0b0_0000_0000_0001_0000;


 	private static final int QUICK_PRESENTER_START= SHOW_SOURCE_OUTLINE;
 	private static final int QUICK_PRESENTER_END= SHOW_ELEMENT_HIERARCHY;


 	private final int flags;

 	private int lastSentSelectionOffset;
 	private int lastSentSelectionLength;

 	private IInformationPresenter sourceOutlinePresenter;
 	private IInformationPresenter elementOutlinePresenter;
 	private IInformationPresenter elementHierarchyPresenter;


 	public SourceEditorViewer(final Composite parent, final IVerticalRuler ruler,
 			final IOverviewRuler overviewRuler, final boolean showsAnnotationOverview, final int styles,
 			final int flags) {
 		super(parent, ruler, overviewRuler, showsAnnotationOverview, styles);
 		this.flags= flags;

 		addPostSelectionChangedListener(new ISelectionChangedListener() {
 			/**
 			 * By default source viewers do not caret changes to selection change listeners, only
 			 * to post selection change listeners.  This sents these post selection changes after
 			 * validation to the selection change listeners too.
 			 */
 			@Override
 			public void selectionChanged(final SelectionChangedEvent event) {
 				final ITextSelection selection= (ITextSelection) event.getSelection();
 				if (SourceEditorViewer.this.lastSentSelectionOffset != selection.getOffset()
 						|| SourceEditorViewer.this.lastSentSelectionLength != selection.getLength()) {
 					final Point currentSelection= getSelectedRange();
 					if (currentSelection.x == selection.getOffset() && currentSelection.y == selection.getLength()) {
 						fireSelectionChanged(currentSelection.x, currentSelection.y);
 					}
 				}
 			}
 		});
 	}


 	@Override
 	protected void fireSelectionChanged(final SelectionChangedEvent event) {
 		final ITextSelection selection= (ITextSelection) event.getSelection();
 		this.lastSentSelectionOffset= selection.getOffset();
 		this.lastSentSelectionLength= selection.getLength();

 		super.fireSelectionChanged(event);
 	}


 	private IInformationPresenter getPresenter(final int operation) {
 		switch (operation) {
 		case SHOW_SOURCE_OUTLINE:
 			return this.sourceOutlinePresenter;
 		case SHOW_ELEMENT_OUTLINE:
 			return this.elementOutlinePresenter;
 		case SHOW_ELEMENT_HIERARCHY:
 			return this.elementHierarchyPresenter;
 		default:
 			return null;
 		}
 	}

 	private void setPresenter(final int operation, final IInformationPresenter presenter) {
 		switch (operation) {
 		case SHOW_SOURCE_OUTLINE:
 			this.sourceOutlinePresenter= presenter;
 			return;
 		case SHOW_ELEMENT_OUTLINE:
 			this.elementOutlinePresenter= presenter;
 			return;
 		case SHOW_ELEMENT_HIERARCHY:
 			this.elementHierarchyPresenter= presenter;
 			return;
 		default:
 			if (presenter != null) {
 				presenter.uninstall();
 			}
 			return;
 		}
 	}

 	@Override
 	public boolean canDoOperation(final int operation) {
 		switch (operation) {
 		case SHOW_SOURCE_OUTLINE:
 		case SHOW_ELEMENT_OUTLINE:
 		case SHOW_ELEMENT_HIERARCHY:
 			return (getPresenter(operation) != null);
 		default:
 			return super.canDoOperation(operation);
 		}
 	}

 	@Override
 	public void doOperation(final int operation) {
 		switch (operation) {
 		case SHOW_SOURCE_OUTLINE:
 		case SHOW_ELEMENT_OUTLINE:
 		case SHOW_ELEMENT_HIERARCHY: {
 			final IInformationPresenter presenter= getPresenter(operation);
 			if (presenter != null) {
 				presenter.showInformation();
 			}
 			return; }
 		default:
 			super.doOperation(operation);
 			return;
 		}
 	}

 	@Override
 	public void configure(final SourceViewerConfiguration configuration) {
 		super.configure(configuration);

 		if (configuration instanceof SourceEditorViewerConfiguration) {
 			for (int operation= QUICK_PRESENTER_START; operation < QUICK_PRESENTER_END; operation++) {
 				final IInformationPresenter presenter= ((SourceEditorViewerConfiguration) configuration).getQuickPresenter(this, operation);
 				if (presenter != null) {
 					presenter.install(this);
 				}
 				setPresenter(operation, presenter);
 			}
 		}
 	}

 	@Override
 	public void unconfigure() {
 		for (int operation= QUICK_PRESENTER_START; operation < QUICK_PRESENTER_END; operation++) {
 			final IInformationPresenter presenter= getPresenter(operation);
 			if (presenter != null) {
 				presenter.uninstall();
 				setPresenter(operation, null);
 			}
 		}

 		super.unconfigure();
 	}

 	public String[] getDefaultPrefixes(final String contentType) {
 		return (this.fDefaultPrefixChars != null) ?
 				(String[]) this.fDefaultPrefixChars.get(contentType) :
 				null;
 	}


 /*[ Workaround for E-Bug 480312 ]==============================================*/


 	private final class ViewerState {

 		/** The position tracking the selection. */
 		private Position selection;

 		/** The position tracking the visually stable line. */
 		private Position stableLine;
 		/** The pixel offset of the stable line measured from the client area. */
 		private int stablePixel;

 		/** The position updater for {@link #selection} and {@link #stableLine}. */
 		private IPositionUpdater updater;
 		/** The document that the position updater and the positions are registered with. */
 		private IDocument updaterDocument;
 		/** The position category used by {@link #updater}. */
 		private String updaterCategory;

 		private int topPixel;


 		/**
 		 * Creates a new viewer state instance and connects it to the current document.
 		 */
 		public ViewerState() {
 			final IDocument document= getDocument();
 			if (document != null) {
 				connect(document);
 			}
 		}


 		public void updateSelection(final int offset, final int length) {
 			if (this.selection == null) {
 				this.selection= new Position(offset, length);
 				if (isConnected()) {
 					try {
 						this.updaterDocument.addPosition(this.updaterCategory, this.selection);
 					}
 					catch (final BadLocationException | BadPositionCategoryException e) {}
 				}
 			}
 			else {
 				updatePosition(this.selection, offset, length);
 			}
 		}

 		/**
 		 * Updates the viewport, trying to keep the
 		 * {@linkplain StyledText#getLinePixel(int) line pixel} of the caret line stable. If the
 		 * selection has been updated while in redraw(false) mode, the new selection is revealed.
 		 */
 		private void updateViewport() {
 			final StyledText textWidget= getTextWidget();
 			if (this.selection != null) {
 				textWidget.setTopPixel(this.topPixel);
 				revealRange(this.selection.getOffset(), this.selection.getLength());
 			}
 			else if (this.stableLine != null) {
 				int stableLine;
 				try {
 					stableLine= this.updaterDocument.getLineOfOffset(this.stableLine.getOffset());
 				}
 				catch (final BadLocationException x) {
 					// ignore and return silently
 					textWidget.setTopPixel(this.topPixel);
 					return;
 				}
 				final int stableWidgetLine= getClosestWidgetLineForModelLine(stableLine);
 				if (stableWidgetLine == -1) {
 					textWidget.setTopPixel(this.topPixel);
 					return;
 				}
 				final int linePixel= textWidget.getLinePixel(stableWidgetLine);
 				final int delta= this.stablePixel - linePixel;
 				final int topPixel= textWidget.getTopPixel();
 				textWidget.setTopPixel(topPixel - delta);
 			}
 		}

 		/**
 		 * Remembers the viewer state.
 		 *
 		 * @param document the document to remember the state of
 		 */
 		private void connect(final IDocument document) {
 			Assert.isLegal(document != null);
 			Assert.isLegal(!isConnected());
 			this.updaterDocument= document;
 			try {
 				final StyledText textWidget= getTextWidget();
 				this.updaterCategory= "ViewerState-" + hashCode();
 				this.updater= new NonDeletingPositionUpdater(this.updaterCategory);
 				this.updaterDocument.addPositionCategory(this.updaterCategory);
 				this.updaterDocument.addPositionUpdater(this.updater);

 				final int stableLine= getStableLine();
 				final int stableWidgetLine= modelLine2WidgetLine(stableLine);
 				this.stablePixel= textWidget.getLinePixel(stableWidgetLine);
 				final IRegion stableLineInfo= this.updaterDocument.getLineInformation(stableLine);
 				this.stableLine= new Position(stableLineInfo.getOffset(), stableLineInfo.getLength());
 				this.updaterDocument.addPosition(this.updaterCategory, this.stableLine);

 				this.topPixel= textWidget.getTopPixel();
 			}
 			catch (final BadPositionCategoryException e) {
 				// cannot happen
 				Assert.isTrue(false);
 			}
 			catch (final BadLocationException e) {
 				// should not happen except on concurrent modification
 				// ignore and disconnect
 				disconnect();
 			}
 		}

 		private void updatePosition(final Position position, final int offset, final int length) {
 			position.setOffset(offset);
 			position.setLength(length);
 			// http://bugs.eclipse.org/bugs/show_bug.cgi?id=32795
 			position.isDeleted= false;
 		}

 		/**
 		 * Returns the document line to keep visually stable. If the caret line is (partially)
 		 * visible, it is returned, otherwise the topmost (partially) visible line is returned.
 		 *
 		 * @return the visually stable line of this viewer state
 		 */
 		private int getStableLine() {
 			int stableLine; // the model line that we try to keep stable
 			final int caretLine= getTextWidget().getLineAtOffset(getTextWidget().getCaretOffset());
 			if (caretLine < JFaceTextUtil.getPartialTopIndex(getTextWidget()) || caretLine > JFaceTextUtil.getPartialBottomIndex(getTextWidget())) {
 				stableLine= JFaceTextUtil.getPartialTopIndex(SourceEditorViewer.this);
 			}
 			else {
 				stableLine= widgetLine2ModelLine(caretLine);
 			}
 			return stableLine;
 		}

 		/**
 		 * Returns <code>true</code> if the viewer state is being tracked, <code>false</code>
 		 * otherwise.
 		 *
 		 * @return the tracking state
 		 */
 		private boolean isConnected() {
 			return (this.updater != null);
 		}

 		/**
 		 * Disconnects from the document.
 		 */
 		private void disconnect() {
 			if (isConnected()) {
 				try {
 					this.updaterDocument.removePosition(this.updaterCategory, this.stableLine);
 					this.updaterDocument.removePositionUpdater(this.updater);
 					this.updater= null;
 					this.updaterDocument.removePositionCategory(this.updaterCategory);
 					this.updaterCategory= null;
 				}
 				catch (final BadPositionCategoryException x) {
 					// cannot happen
 					Assert.isTrue(false);
 				}
 			}
 		}
 	}


 	private ViewerState viewerState;


 	@Override
 	protected void disableRedrawing() {
 		if ((this.flags & VARIABLE_LINE_HEIGHT) != 0) {
 			this.viewerState= new ViewerState();
 		}

 		super.disableRedrawing();
 	}

 	@Override
 	protected void enabledRedrawing(final int topIndex) {
 		super.enabledRedrawing(topIndex);

 		if (this.viewerState != null) {
 			this.viewerState.disconnect();
 			if (topIndex == -1) {
 				this.viewerState.updateViewport();
 			}
 			this.viewerState= null;
 		}
 	}

 	@Override
 	public void setSelectedRange(final int selectionOffset, final int selectionLength) {
 		if (this.viewerState != null && !redraws()) {
 			this.viewerState.updateSelection(selectionOffset, selectionLength);
 			return;
 		}

 		super.setSelectedRange(selectionOffset, selectionLength);
 	}

 }
	/*=============================================================================#
	# Copyright (c) 2013, 2020 Stephan Wahlbrink and others.
	#
	# This program and the accompanying materials are made available under the
	# terms of the Eclipse Public License 2.0 which is available at
	# https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
	# which is available at https://www.apache.org/licenses/LICENSE-2.0.
	#
	# SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
	#
	# Contributors:
	# Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
	#=============================================================================*/

	package org.eclipse.statet.ltk.ui.sourceediting;

	import org.eclipse.core.runtime.Assert;
	import org.eclipse.jface.text.BadLocationException;
	import org.eclipse.jface.text.BadPositionCategoryException;
	import org.eclipse.jface.text.IDocument;
	import org.eclipse.jface.text.IPositionUpdater;
	import org.eclipse.jface.text.IRegion;
	import org.eclipse.jface.text.ITextSelection;
	import org.eclipse.jface.text.JFaceTextUtil;
	import org.eclipse.jface.text.Position;
	import org.eclipse.jface.text.information.IInformationPresenter;
	import org.eclipse.jface.text.source.IOverviewRuler;
	import org.eclipse.jface.text.source.IVerticalRuler;
	import org.eclipse.jface.text.source.SourceViewerConfiguration;
	import org.eclipse.jface.text.source.projection.ProjectionViewer;
	import org.eclipse.jface.viewers.ISelectionChangedListener;
	import org.eclipse.jface.viewers.SelectionChangedEvent;
	import org.eclipse.swt.custom.StyledText;
	import org.eclipse.swt.graphics.Point;
	import org.eclipse.swt.widgets.Composite;

	import org.eclipse.statet.ecommons.text.core.util.NonDeletingPositionUpdater;


	public class SourceEditorViewer extends ProjectionViewer {


	/**
	* Text operation code for requesting the outline for the current input.
	*/
	public static final int SHOW_SOURCE_OUTLINE= 51;

	/**
	* Text operation code for requesting the outline for the element at the current position.
	*/
	public static final int SHOW_ELEMENT_OUTLINE= 52;

	/**
	* Text operation code for requesting the hierarchy for the current input.
	*/
	public static final int SHOW_ELEMENT_HIERARCHY= 53;


	public static final int VARIABLE_LINE_HEIGHT= 0b0_0000_0000_0001_0000;


	private static final int QUICK_PRESENTER_START= SHOW_SOURCE_OUTLINE;
	private static final int QUICK_PRESENTER_END= SHOW_ELEMENT_HIERARCHY;


	private final int flags;

	private int lastSentSelectionOffset;
	private int lastSentSelectionLength;

	private IInformationPresenter sourceOutlinePresenter;
	private IInformationPresenter elementOutlinePresenter;
	private IInformationPresenter elementHierarchyPresenter;


	public SourceEditorViewer(final Composite parent, final IVerticalRuler ruler,
	final IOverviewRuler overviewRuler, final boolean showsAnnotationOverview, final int styles,
	final int flags) {
	super(parent, ruler, overviewRuler, showsAnnotationOverview, styles);
	this.flags= flags;

	addPostSelectionChangedListener(new ISelectionChangedListener() {
	/**
	* By default source viewers do not caret changes to selection change listeners, only
	* to post selection change listeners. This sents these post selection changes after
	* validation to the selection change listeners too.
	*/
	@Override
	public void selectionChanged(final SelectionChangedEvent event) {
	final ITextSelection selection= (ITextSelection) event.getSelection();
	if (SourceEditorViewer.this.lastSentSelectionOffset != selection.getOffset()
	\|\| SourceEditorViewer.this.lastSentSelectionLength != selection.getLength()) {
	final Point currentSelection= getSelectedRange();
	if (currentSelection.x == selection.getOffset() && currentSelection.y == selection.getLength()) {
	fireSelectionChanged(currentSelection.x, currentSelection.y);
	}
	}
	}
	});
	}


	@Override
	protected void fireSelectionChanged(final SelectionChangedEvent event) {
	final ITextSelection selection= (ITextSelection) event.getSelection();
	this.lastSentSelectionOffset= selection.getOffset();
	this.lastSentSelectionLength= selection.getLength();

	super.fireSelectionChanged(event);
	}


	private IInformationPresenter getPresenter(final int operation) {
	switch (operation) {
	case SHOW_SOURCE_OUTLINE:
	return this.sourceOutlinePresenter;
	case SHOW_ELEMENT_OUTLINE:
	return this.elementOutlinePresenter;
	case SHOW_ELEMENT_HIERARCHY:
	return this.elementHierarchyPresenter;
	default:
	return null;
	}
	}

	private void setPresenter(final int operation, final IInformationPresenter presenter) {
	switch (operation) {
	case SHOW_SOURCE_OUTLINE:
	this.sourceOutlinePresenter= presenter;
	return;
	case SHOW_ELEMENT_OUTLINE:
	this.elementOutlinePresenter= presenter;
	return;
	case SHOW_ELEMENT_HIERARCHY:
	this.elementHierarchyPresenter= presenter;
	return;
	default:
	if (presenter != null) {
	presenter.uninstall();
	}
	return;
	}
	}

	@Override
	public boolean canDoOperation(final int operation) {
	switch (operation) {
	case SHOW_SOURCE_OUTLINE:
	case SHOW_ELEMENT_OUTLINE:
	case SHOW_ELEMENT_HIERARCHY:
	return (getPresenter(operation) != null);
	default:
	return super.canDoOperation(operation);
	}
	}

	@Override
	public void doOperation(final int operation) {
	switch (operation) {
	case SHOW_SOURCE_OUTLINE:
	case SHOW_ELEMENT_OUTLINE:
	case SHOW_ELEMENT_HIERARCHY: {
	final IInformationPresenter presenter= getPresenter(operation);
	if (presenter != null) {
	presenter.showInformation();
	}
	return; }
	default:
	super.doOperation(operation);
	return;
	}
	}

	@Override
	public void configure(final SourceViewerConfiguration configuration) {
	super.configure(configuration);

	if (configuration instanceof SourceEditorViewerConfiguration) {
	for (int operation= QUICK_PRESENTER_START; operation < QUICK_PRESENTER_END; operation++) {
	final IInformationPresenter presenter= ((SourceEditorViewerConfiguration) configuration).getQuickPresenter(this, operation);
	if (presenter != null) {
	presenter.install(this);
	}
	setPresenter(operation, presenter);
	}
	}
	}

	@Override
	public void unconfigure() {
	for (int operation= QUICK_PRESENTER_START; operation < QUICK_PRESENTER_END; operation++) {
	final IInformationPresenter presenter= getPresenter(operation);
	if (presenter != null) {
	presenter.uninstall();
	setPresenter(operation, null);
	}
	}

	super.unconfigure();
	}

	public String[] getDefaultPrefixes(final String contentType) {
	return (this.fDefaultPrefixChars != null) ?
	(String[]) this.fDefaultPrefixChars.get(contentType) :
	null;
	}


	/[ Workaround for E-Bug 480312 ]==============================================/


	private final class ViewerState {

	/** The position tracking the selection. */
	private Position selection;

	/** The position tracking the visually stable line. */
	private Position stableLine;
	/** The pixel offset of the stable line measured from the client area. */
	private int stablePixel;

	/** The position updater for {@link #selection} and {@link #stableLine}. */
	private IPositionUpdater updater;
	/** The document that the position updater and the positions are registered with. */
	private IDocument updaterDocument;
	/** The position category used by {@link #updater}. */
	private String updaterCategory;

	private int topPixel;


	/**
	* Creates a new viewer state instance and connects it to the current document.
	*/
	public ViewerState() {
	final IDocument document= getDocument();
	if (document != null) {
	connect(document);
	}
	}


	public void updateSelection(final int offset, final int length) {
	if (this.selection == null) {
	this.selection= new Position(offset, length);
	if (isConnected()) {
	try {
	this.updaterDocument.addPosition(this.updaterCategory, this.selection);
	}
	catch (final BadLocationException \| BadPositionCategoryException e) {}
	}
	}
	else {
	updatePosition(this.selection, offset, length);
	}
	}

	/**
	* Updates the viewport, trying to keep the
	* {@linkplain StyledText#getLinePixel(int) line pixel} of the caret line stable. If the
	* selection has been updated while in redraw(false) mode, the new selection is revealed.
	*/
	private void updateViewport() {
	final StyledText textWidget= getTextWidget();
	if (this.selection != null) {
	textWidget.setTopPixel(this.topPixel);
	revealRange(this.selection.getOffset(), this.selection.getLength());
	}
	else if (this.stableLine != null) {
	int stableLine;
	try {
	stableLine= this.updaterDocument.getLineOfOffset(this.stableLine.getOffset());
	}
	catch (final BadLocationException x) {
	// ignore and return silently
	textWidget.setTopPixel(this.topPixel);
	return;
	}
	final int stableWidgetLine= getClosestWidgetLineForModelLine(stableLine);
	if (stableWidgetLine == -1) {
	textWidget.setTopPixel(this.topPixel);
	return;
	}
	final int linePixel= textWidget.getLinePixel(stableWidgetLine);
	final int delta= this.stablePixel - linePixel;
	final int topPixel= textWidget.getTopPixel();
	textWidget.setTopPixel(topPixel - delta);
	}
	}

	/**
	* Remembers the viewer state.
	*
	* @param document the document to remember the state of
	*/
	private void connect(final IDocument document) {
	Assert.isLegal(document != null);
	Assert.isLegal(!isConnected());
	this.updaterDocument= document;
	try {
	final StyledText textWidget= getTextWidget();
	this.updaterCategory= "ViewerState-" + hashCode();
	this.updater= new NonDeletingPositionUpdater(this.updaterCategory);
	this.updaterDocument.addPositionCategory(this.updaterCategory);
	this.updaterDocument.addPositionUpdater(this.updater);

	final int stableLine= getStableLine();
	final int stableWidgetLine= modelLine2WidgetLine(stableLine);
	this.stablePixel= textWidget.getLinePixel(stableWidgetLine);
	final IRegion stableLineInfo= this.updaterDocument.getLineInformation(stableLine);
	this.stableLine= new Position(stableLineInfo.getOffset(), stableLineInfo.getLength());
	this.updaterDocument.addPosition(this.updaterCategory, this.stableLine);

	this.topPixel= textWidget.getTopPixel();
	}
	catch (final BadPositionCategoryException e) {
	// cannot happen
	Assert.isTrue(false);
	}
	catch (final BadLocationException e) {
	// should not happen except on concurrent modification
	// ignore and disconnect
	disconnect();
	}
	}

	private void updatePosition(final Position position, final int offset, final int length) {
	position.setOffset(offset);
	position.setLength(length);
	// http://bugs.eclipse.org/bugs/show_bug.cgi?id=32795
	position.isDeleted= false;
	}

	/**
	* Returns the document line to keep visually stable. If the caret line is (partially)
	* visible, it is returned, otherwise the topmost (partially) visible line is returned.
	*
	* @return the visually stable line of this viewer state
	*/
	private int getStableLine() {
	int stableLine; // the model line that we try to keep stable
	final int caretLine= getTextWidget().getLineAtOffset(getTextWidget().getCaretOffset());
	if (caretLine < JFaceTextUtil.getPartialTopIndex(getTextWidget()) \|\| caretLine > JFaceTextUtil.getPartialBottomIndex(getTextWidget())) {
	stableLine= JFaceTextUtil.getPartialTopIndex(SourceEditorViewer.this);
	}
	else {
	stableLine= widgetLine2ModelLine(caretLine);
	}
	return stableLine;
	}

	/**
	* Returns <code>true</code> if the viewer state is being tracked, <code>false</code>
	* otherwise.
	*
	* @return the tracking state
	*/
	private boolean isConnected() {
	return (this.updater != null);
	}

	/**
	* Disconnects from the document.
	*/
	private void disconnect() {
	if (isConnected()) {
	try {
	this.updaterDocument.removePosition(this.updaterCategory, this.stableLine);
	this.updaterDocument.removePositionUpdater(this.updater);
	this.updater= null;
	this.updaterDocument.removePositionCategory(this.updaterCategory);
	this.updaterCategory= null;
	}
	catch (final BadPositionCategoryException x) {
	// cannot happen
	Assert.isTrue(false);
	}
	}
	}
	}


	private ViewerState viewerState;


	@Override
	protected void disableRedrawing() {
	if ((this.flags & VARIABLE_LINE_HEIGHT) != 0) {
	this.viewerState= new ViewerState();
	}

	super.disableRedrawing();
	}

	@Override
	protected void enabledRedrawing(final int topIndex) {
	super.enabledRedrawing(topIndex);

	if (this.viewerState != null) {
	this.viewerState.disconnect();
	if (topIndex == -1) {
	this.viewerState.updateViewport();
	}
	this.viewerState= null;
	}
	}

	@Override
	public void setSelectedRange(final int selectionOffset, final int selectionLength) {
	if (this.viewerState != null && !redraws()) {
	this.viewerState.updateSelection(selectionOffset, selectionLength);
	return;
	}

	super.setSelectedRange(selectionOffset, selectionLength);
	}

	}